An exception of type Microsoft.SharePoint.PostSetupConfiguration.PostSetupConfigurationTaskException was thrown. Additional exception information: The pre-upgrade scan tool has not yet been run successfully on all content databases in the server farm. The pre-upgrade scan tool must complete without errors before you can continue with the upgrade process.

The prescan tool not only tells you if there are things affecting upgrade, but sets a value in the content database that the upgrade looks for in order to be assured that the upgrade to the content database can take place with no errors.